He's actually one of the very few characters in the universe who is completely sane. He is almost alone in not suffering from the delusion that he isn't a comic character, and the reason he acts the way he does is that he has a keen understanding of the way comics work.
Or alternately, he's so insane he loops all the way back to being sane.
Both Deadpool and T Ray are Wade Wilson
Mercedes married a guy named Wade Wilson. Wilson is not such an uncommon name, and neither is Wade. The Wade Wilson she married became T Ray. The name of man saved from the river was not Jack. He was, however, a mercenary. The events T Ray recalled are simply a big misunderstanding, and after he accidentally killed Mercedes, Deadpool went a bit crazy (not insane) and his memor defected so he would think he was Mercedes's husband.